The present invention relates generally to self-supporting fiber optic cables and, more particularly, to self-supporting fiber optic cables having support and cable sections.
Fiber optic cables can be employed in a variety of applications including the transmission of voice, video and data in cable television, computer and telephone systems. Regardless of the application, fiber optic cables are typically installed either in conduits that are disposed within the ground, or aerially by being strung between utility poles or the like. Of the aerially installed fiber optic cables, self-supporting fiber optic cables are advantageous since self-supporting fiber optic cables include both optical fibers as well as the support member for providing mechanical support for the aerially installed cable.
Self-supporting fiber optic cables typically include a support section for supporting the fiber optic cable and a cable section that includes optical fibers, or a combination of optical fibers and electrical conductors. While self-supporting fiber optic cables have been designed that have various profiles, one type of self-supporting fiber optic cable is a xe2x80x9cFigure 8xe2x80x9d configuration. As its name suggests, a xe2x80x9cFigure 8xe2x80x9dself-supporting fiber optic cable includes a pair of lobes connected by a web, wherein the support section forms one of the lobes and the cable section forms the other lobe.
The cable section of a conventional self-supporting fiber optic cable includes one or more buffer tubes in which the optical fibers, or a combination of optical fibers and electrical conductors, are disposed. In addition, the cable section can include one or more lengthwise extending strength members. For example, the cable section can include a plurality of buffer tubes helically stranded about a central strength member so as to define an SZ pattern or the like. Alternatively, the cable section can be of a monotube design having a single buffer tube and one or, more typically, a pair of strength members extending lengthwise along opposite sides of the buffer tube. In either design, the cable section also includes a jacket surrounding the buffer tubes and the strength members for protecting the cable components from environmental degradation and the like.
The support section of a conventional self-supporting fiber optic cable includes at least one and, more commonly, a plurality of strength members. For example, a support section can include a plurality of helically wound wires, such as galvanized steel wires. Like the cable section, the support section also includes a continuous jacket that surrounds the strength members along their entire length for protecting the strength members from environmental degradation and the like. In order to prevent water migration through the support section that could corrode the strength members, the strength members are generally asphalt flooded or are otherwise treated to prevent water migration.
The web connects the jackets of the support section and the cable section. The web typically extends continuously along the length of the fiber optic cable in the same fashion that the jackets of the support section and the cable section extend continuously along the length of the fiber optic cable. However, fiber optic cables have been designed that include an intermittent web that only connects the support and cable sections at discrete points along the length of the fiber optic cable. Among other things, an intermittent web permits the cable section to flex or bend relative to the support section, such as in instances in which the cable section is designed to have an overlength with respect to the support section in order to accommodate some elongation of the support section in response to tensile forces placed upon the cable without subjecting the optical fibers of the cable section to the tensile forces. In addition, an intermittent web permits at least some wind to pass through the windows defined between adjacent web segments in order to decrease the wind loading otherwise experienced by the fiber optic cable. Still further, an intermittent web decreases the weight of the fiber optic cable. Since the weight of a fiber optic cable contributes to the tensile forces experienced by an aerially installed fiber optic cable, any decrease in the weight of a fiber optic cable is advantageous. In any event, the web is generally extruded concurrent with the extrusion of the jackets of the support section and the cable section such that the web, albeit a continuous web or an intermittent web, is integral with the jackets of the support section and the cable section.
Even in instances in which a self-supporting fiber optic cable includes an intermittent web, the jackets of the support section and the cable section are continuous in order to protect the strength members and the optical fibers from environmental degradation and the like. During installation of a self-supporting fiber optic cable, however, the jacket of the support section must sometimes be removed from those portions of the fiber optic cable proximate a point of attachment to permit the strength members of the support section to be securely gripped. For example, during installations in which a fiber optic cable is going to turn around a comer or otherwise be redirected, the strength members of the support section are typically connected to a utility pole at or near the comer by means of a preform or some other type of connector hardware. In order to securely grip the strength members of the support section, the jacket surrounding the strength members is typically removed from that portion of the strength members that will be gripped by the preform or other connector hardware. As will be apparent, the time and labor required to strip the jacket from the portion of the support section that will be attached to a utility pole or the like increases the time required for installation and the resulting cost of the self-supporting fiber optic cable. With the ever increasing demands to reduce the cost of fiber optic cable, any increase in the material or installation costs of the fiber optic cable is particularly disadvantageous.
An improved self-supporting fiber optic cable is therefore provided for aerial applications. The fiber optic cable includes a cable section comprising at least one optical fiber and a jacket surrounding the at least one optical fiber; and a support section comprising at least one strength member extending in a lengthwise direction and a jacket surrounding portions of the at least one strength member and connected to the jacket of the cable section by webs, wherein the jacket of the support section comprises a plurality of jacket segments spaced lengthwise along the at least one strength member. Preferably, the jacket segments are monolithically formed with the webs and the segments are separated by wholly or at least partially exposed portions of the strength member. Moreover, the segments can be connected to other segments by a thin coating between the segments monolithically formed with the segments.
In another aspect of the present invention, a fiber optic cable includes a cable section including at least one optical fiber and a jacket surrounding the at least one optical fiber; a support section including at least one strength member and a jacket surrounding portions of the at least one strength member; and a web connecting the respective jackets of the cable section and the support section, wherein the web and the jacket of the support section have a plurality of web and jacket segments, respectively, disposed in a spaced relationship. As such, portions of the at least one strength member are wholly or partially exposed between the plurality of jacket segments.
In preferred embodiments, each pair of adjacent jacket segments are spaced apart by a distance greater than the length of either jacket segment taken in a lengthwise direction, thereby reducing the material cost and the weight of the fiber optic cable of the present invention in comparison to a comparable fiber optic cable of conventional design having a support section with a continuous jacket having a constant thickness or outside diameter. Since a substantial portion of the strength members of the support section can be wholly or at least partially exposed or thinly coated between adjacent jacket segments, the jacket of the support section will likely not have to be removed as frequently during installation since those portions of the strength members that are already exposed can be gripped without removing the jacket segments. Where the support wire is wholly or partially exposed, however, the strength members are preferably comprised of a material, such as galvanized steel, that is environmentally stable, e.g., corrosion resistant.
According to another aspect of the present invention, a method of manufacturing a fiber optic cable is disclosed that provides at least one optical fiber and at least one strength member, and that extrudes jackets thereabout to define a cable section including the at least one optical fiber and a support section including the at least one strength member, wherein the extrusion of the jacket about the at least one strength member is controlled to define a plurality of jacket segments spaced apart along the at least one strength member such that portions of the at least one strength member are wholly or partially, or thinly coated, exposed between the plurality of jacket segments.